The present invention generally relates to the installation of electric lighting fixtures, and more particularly to the installation of ceiling suspended lighting fixtures having electrical power cords that must be extended between the fixtures and the overhead ceiling.
Lighting designs for architectural spaces frequently include lighting fixtures suspended from an overhead ceiling structure where the lighting fixtures become an architectural element within the space. In office environments, a typical lighting installation will include the suspension of runs of direct or indirect, or direct/indirect, lighting fixtures below a ceiling such as a grid ceiling from multiple suspension points located on the ceiling. Each run of fixtures will require at least one power feed location where a potentially unsightly power cord must be run from the lighting fixture up to an electrical junction box above the ceiling. In older installations, the runs of lighting fixtures were often suspended by rigid hollow stems which permitted the fixture's power cord to be fed through the stem at the power feed locations. The rigid stems concealed the power cords and provided a clean, finished look to the installation. However, rigid stem designs became impractical with the introduction of earthquake building codes in earthquake-prone areas, such as California, which require that a fixture be allowed to sway during a seismic event.
One response to earthquake codes was to use ball stems having a ball joint that permitted a suitable swivel motion about the stem. This solution preserved the advantage of being able to hide the power cord since, like rigid stems, ball stems are hollow so that the power cord can be passed through the stems. However, ball stems are relatively costly and difficult to install. As a result, aircraft cable is now widely used to suspend lighting fixtures from overhead ceiling structures. Aircraft cable has a high degree of flexibility and has high tensile strength. It is also inexpensive and easy to install, and allows the fixture the freedom to sway, thereby meeting earthquake codes.
The problem with aircraft cable is that the power cords for electrifying the lighting fixtures must be dropped next to the cable. Power cords are visually objectionable and detract from the finished appearance of lighting installation. To mitigate this problem, different techniques have been devised to hold the power cord next to the aircraft cable so that the power cord runs parallel to the cable. Such techniques include the use of cable ties or clips, and cord managers such as disclosed in U.S. Pat. No. 6,428,190. However, ties, clips and cord managers fail to hide the power cord and themselves create visual detractions. Cord managers can also inhibit the ability of the fixture to sway during seismic events.
To overcome the objections to external power cords, a hanger system has been devised that is both flexible and hides the power cord within the hanger. In this prior hanger design, the electrical wiring is encased in an outer metal flexible sheath with attachment hardware connected to the ends of the sheath that allow the hanger to be attached to the lighting fixture at one end and to a junction box in the overhead ceiling at the other. The difficulty with this solution is that the connections between the attachment hardware and the flexible outer sheath create structural weak points along the length of the hanger, which compromise the hanger's load bearing capacity. Also, while having a degree of flexibility, the metal sheath is not sufficiently flexible to allow the suspended fixture to experience a large degree of sway, with the sway generally being limited to a range of around +/−10 degrees from vertical.